msgbuf: Rename 'destroy' APIs to 'complete'

Change the language to better reflect the intent, with the impending
introduction of the ability to 'discard' a msgbuf instance.

Change-Id: Idbb79dcc2587a8baef67ffd405e0bc77e66fe995
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/src/firmware_device/fd.c b/src/firmware_device/fd.c
index d43b6cc..9ac1ab8 100644
--- a/src/firmware_device/fd.c
+++ b/src/firmware_device/fd.c
@@ -363,8 +363,8 @@
 		}
 	}
 
-	return pldm_msgbuf_destroy_used(buf, *resp_payload_len,
-					resp_payload_len);
+	return pldm_msgbuf_complete_used(buf, *resp_payload_len,
+					 resp_payload_len);
 }
 
 LIBPLDM_CC_NONNULL